Steam Turbine Performance Examples

Two sets of examples are provided to demonstrate the principles of steam turbine operation. The examples demonstrate actual and ideal cycle efficiencies for both condensing and back-pressure turbines. They also include a comparison of the thermodynamics associated with using a back-pressure turbine in place of a pressure reducing valve (PRV).

In all cases, available enthalpy drop and the turbine mechanical efficiency determine the amount of power that can be produced. It is clear that the higher pressure and temperature steam condition in Examples 4 to 6 produce greater simple-cycle efficiency and significantly more power output for a given steam flow. In the case of the back-pressure turbine, the ideal and actual net thermal efficiency in both examples are shown to be approximately equal to the boiler thermal fuel efficiency of 85%, confirming the high efficiency achieved with a topping cycle.

Values are given in English system units. Refer to Conversion Tables in Chapter 6 for SI unit equivalents.

s = ENTROPY

Fig. 11-45 Temperature-Entropy Diagram of Rankine Cycle for Wet, Dry Saturated and Superheated Steam. Source: Babcock & Wilcox s = ENTROPY

Fig. 11-45 Temperature-Entropy Diagram of Rankine Cycle for Wet, Dry Saturated and Superheated Steam. Source: Babcock & Wilcox

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